A Blend of Two Circadian Clocks, Seasoned to Perfection

The daily activity of the fruit fly Drosophila is controlled by both a “morning” and an “evening” circadian clock. In this issue demonstrate that day length determines which clock dominates the neural circuitry governing circadian behavior. Thus, these findings suggest a mechanism by which the system for circadian timing adapts to changes in the seasons to impose appropriate rhythms of daily activity.